1. Field of the Invention
The present invention relates to a transmission type liquid crystal display device and various types of optical display devices for guiding color display lights emitted from a light emitting portion having at least two or more illuminants having different peak wavelengths, for example, a red illuminant, a green illuminant, and a blue illuminant to a display portion through a light guiding plate provided on a back face side of the display portion in order to perform color display.
2. Description of the Related Art
For example, in a transmission type or semi-transmission type liquid crystal display device, a back face of a display panel unit having a liquid crystal panel is combined with a display light guiding optical unit having a light guiding plate, a light diffusion plate, a reflecting plate (reflecting sheet), or the like. Color display lights are made incident from a light emitting portion having a red illuminant, a green illuminant, and a blue illuminant to the display light guiding optical unit. A light emitting diode (LED), for example, having high luminance characteristics, low power consumption characteristics, long life characteristics, or the like has been used as a light emitting source in the liquid crystal display device. In the liquid crystal display device, a red display light, a green display light, and a blue display light which are emitted from a red LED, a green LED, and a blue LED, respectively, are mixed with one another within a light guiding plate to turn into a white display light. The resulting white display light is guided from the light guiding plate to a display panel unit. The liquid crystal display device controls transmission and light shielding of the white display light in the display panel unit, so that predetermined color display is performed.
Now, in the liquid crystal display device using the LEDs or light sources, the light emission states of the red LED, the green LED, and the blue LED are changed due to a change in an ambient temperature, a dispersion of products, a large term change, and the like. As a result, there is caused a problem such that a white balance among the display lights is lost, and thus a dispersion occurs in a luminance and a color tone. Therefore, in order to cope with this problem, the liquid crystal display device is provided with a light detecting sensor for detecting the states of the display lights. Also, the light emission states of the red LED, the green LED, and the blue LED are controlled in accordance with a detection signal outputted from the light detecting sensor. This technique, for example, is disclosed in Japanese Patent Laid-open Nos. 2005-71702 and 2005-91526.
That is to say, in a liquid crystal display device 100 of a related art, as shown in FIGS. 12 and 13, a display panel unit 102 having a liquid crystal panel (the details of which are omitted here) is assembled in a frame 101. Also, a backlight unit 103 is assembled in the frame 101 so as to be located on a back face side of a display panel unit 102. The backlight unit 103 includes a display light guiding optical unit 104, a light emitting portion 105 for emitting display lights, a detection portion 106 for detecting states of the display lights, and the like. In the backlight unit 103, the display light guiding optical unit 104 has a light guiding plate 107, a reflecting plate (reflecting sheet) 108, or a diffusion sheet (not shown), and the like. Here, the light guiding plate 107 is combined with a back face of the display panel unit 102 so as to face the back face of the display panel unit 102. Also, the reflecting plate 108 is combined with a back face of the light guiding plate 107 so as to face the back face of the light guiding plate 107.
In the backlight unit 103, the light emitting portion 105 includes a plurality of light emitting units 110 having a red LED 109R, a green LED 109G, and a blue LED 109B (hereinafter generally referred to as “LEDs 109” except for individual description thereof). In the light emitting portion 105, the light emitting units 110 are installed in an LED flexible wiring board 111 which is attached to the frame 101 so as to be located in a lower portion of the display panel unit 102. Also, in the light emitting portion 105, the light emitting units 110 are installed on the LED flexible wiring board 111 so that light emission surfaces of the LEDs 109, as shown in FIG. 13, face a lower end face 107A of the light guiding plate 107.
In the backlight unit 103, driving voltages are supplied from an LED driving circuit portion 112 to the LEDs 109, respectively, through the LED flexible wiring board 111, so that the LEDs 109 are turned on to emit a red display light, a green display light, and a blue display light, respectively. In the backlight unit 103, the display lights emitted from the LEDs 109, respectively, are made incident from the lower end face 107A of the light guiding plate 107 to the inside of the light guiding plate 107. Also, the display lights are mixed with one another in the inside of the light guiding plate 107 to turn into a white display light and the resulting white display light is supplied to the display panel unit 102.
In the backlight unit 103, the detection portion 106 detects the states of the display lights, and as shown in FIG. 12, outputs a detection signal to a controller 113. The detection portion 106 is disposed in the frame 101 so as to be located in an upper portion of the display panel unit 102 and so as to face the above-mentioned light emitting portion 105. Also, the detection portion 106 includes a red sensor 114R, a green sensor 114G, and a blue sensor 114B (hereinafter generally referred to as “color sensors 114” except for individual description thereof). The color sensors 114 of the detection portion 106 are mounted on a sensor flexible wiring board 115 so that their light receiving portions face an upper end face 107B of the light guiding plate 107.
In the liquid crystal display device 100 constructed as described above, a part of the white display light which is guided to the inside of the light guiding plate 107 leaks from the upper end face 107B. The leakage white display light is detected by the detection portion 106. In the liquid crystal display device 100, for example, the controller 113 determines a red component, a green component, and a blue component, of the white display light, which are detected by the respective color sensors 114 of the detection portion 106. Then, the controller 113 outputs a control signal to the LED driving circuit portion 112. As a result, in the liquid crystal display device 100, the turn-on states of the LEDs 109 are controlled, and the luminance and the color tone are controlled so that the white display light in which the balance among the red component, the green component, and the blue component is optimized is supplied to the display panel unit 102.